Method of providing and evaluating a mid-wall repair

ABSTRACT

A method of repairing and inspecting a first nozzle penetrating a closed vessel. The method includes removing a portion of the first nozzle, and forming a weld between a replacement nozzle and a surface of the mid-wall of the vessel. The method further includes evaluating the integrity of the weld at the mid-wall of the vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 11/091,767, filed Mar. 29, 2005, the contents of which areincorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention is directed to a method of providing a mid-wallrepair, as well as a method of evaluating the mid-wall repair.

DISCUSSION OF THE RELATED ART

In pressurized water (PWR) and boiling water (BWR) nuclear reactors,multiple penetrations are provided in a pressure vessel or piping. Thepenetrations consist of sleeves and/or nozzles that extend from theexterior of the pressure vessel through openings in a low alloy orcarbon steel vessel wall and a nickel-chromium-iron (Ni—Cr—Fe) orstainless steel clad disposed on the interior surface of the pressurevessel. During initial fabrication (i.e., before access to the interiorof the pressure vessel is limited, and before the pressure vessel issubjected to radiation and pressurized high temperature water as aresult of operation of the nuclear reactor), a J-shaped groove is formedin the vessel interior clad and in some cases the low alloy steel orcarbon steel vessel interior wall as well, and a weld material isdeposited in the groove to weld the nozzle to the clad and vessel wall,where applicable. Thus, the nozzle is welded from the interior of thepressure vessel to connect the nozzle to the pressure vessel.

As a result of operating and residual stresses in the J-groove weld andthe primary water environment during operation, the welds, the sleevesor nozzles, and the Ni—Cr—Fe or stainless steel cladding are subject tostress corrosion cracking. Thus, it becomes necessary to repair theconnection between the nozzle and the pressure vessel.

In a known repair technique, the technician does not have access to thehighly radioactive interior of the closed pressure vessel. Thus, repairof the connection between the pressure vessel and the nozzle isconducted from the exterior of the pressure vessel.

In the known repair technique, the nozzle is severed at the mid-wall ofthe pressure vessel and a sacrificial plug installed to create a flushsurface at the exterior of the pressure vessel. A welding pad of amaterial that is not susceptible to stress corrosion cracking, such asAlloy 52, is formed on the exterior of the pressure vessel. A hole isdrilled in the welding pad, and a replacement nozzle formed of amaterial that is not susceptible to stress corrosion cracking, such asAlloy 690, is disposed in the hole. The replacement nozzle is thenwelded to the welding pad. Because it is not practical to providepostweld heat treatment stress relief of the weld and the adjacentareas, a temper bead welding technique is used to weld the welding padto the pressure vessel or piping.

The known repair technique suffers from a number of disadvantages,however. These disadvantages include that it is often difficult toprecisely align the replacement nozzle with the openings in the pressurevessel wall and the new welding pad on the pressure vessel. Further, arelatively large amount of material is used to provide the welding padof sufficient size (e.g., 6 inch by 6 inch by 0.5 inch) to permittesting and evaluation of the weld pad to the pressure vessel. Further,because formation of the temper bead must be precisely controlled, theweld pad requires a relatively large amount of time to produce, whichmay increase down time of the nuclear reactor and the amount ofradiation to which the technician is exposed during the repair process.The severity of these problems is compounded by the fact that a typicalpressure vessel includes multiple nozzles.

SUMMARY OF THE INVENTION

Various illustrative embodiments provide a method of repairing andinspecting a first nozzle penetrating a closed vessel. In accordancewith one aspect of an illustrative embodiment, the method may includeremoving a portion of the first nozzle, and forming a weld between areplacement nozzle and a surface of the mid-wall of the vessel. Inaccordance with another aspect of an illustrative embodiment, the methodmay further include evaluating the integrity of the weld at the mid-wallof the vessel.

Various illustrative embodiments of evaluating the integrity of the weldat the mid-wall of the vessel may include performing a liquid penetranttest of the weld; comparing a characteristic of the weld to acharacteristic of at least one of a known defective weld and a knowndefect-free weld; and comparing a characteristic of the weld obtainedthrough ultrasonic inspection

BRIEF DESCRIPTION OF THE DRAWINGS

An appreciation of the present invention, and many of the attendantadvantages of the invention, can be readily ascertained and/or obtainedas the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings, wherein:

FIGS. 1-10 are detail views showing a method of providing and evaluatinga mid-wall repair according to the present invention.

DETAILED DESCRIPTION

Examples of one or more embodiments of the present invention aredescribed with reference to the drawings, wherein like reference numbersthroughout the several views identify like or similar elements.

The method of providing and evaluating a mid-wall repair, as shown inthe drawings and as described herein, can be provided between a pressurevessel or piping 100 (referred to as pressure vessel in the followingdiscussion) of a PWR or BWR nuclear reactor and at least one nozzle 10.It is to be understood, however, that the method can be applied tovarious structures, including various nuclear reactor structures as wellas structures that are not disposed in a nuclear reactor.

As shown in FIG. 1, the pressure vessel 100 can include an interiorsurface 101 opposite an exterior surface 103, and a mid-wall 105extending between the interior and exterior surfaces 101 and 103. Theinterior and exterior surfaces 101 and 103 can be curved or contoured,and the mid-wall 105 can be of a constant thickness, at least in theposition through which the nozzle 10 is disposed. A clad material 107can be disposed on the interior surface 101. In a preferred embodiment,materials of the mid-wall 105 and the clad 107 can include steel, andmore preferably can include a low alloy or carbon steel and an Ni—Cr—Feor stainless steel material, respectively.

As discussed above, the pressure vessel 100 can include at least onenozzle 10. In a preferred embodiment, the pressure vessel 100 caninclude a plurality of nozzles 10. It is to be understood, however, thatthe pressure vessel 100 can include any number of nozzles 10.

As shown in FIG. 2 and FIG. 1, the nozzle 10 can be in the form of asleeve or nozzle having an exterior surface 13 opposite an interiorsurface 15, and a heater or other component 20 disposed within aninterior defined by the interior surface 15 of the nozzle 10. In apreferred embodiment, a material of the nozzle 10 can include an Alloy600 or stainless steel material.

A weld 109 can be used to connect the pressure vessel 100 and the nozzle10. In a preferred embodiment, a groove can be formed in the clad 107 ora combination of the clad and vessel wall with weld butter. Morepreferably, the clad 107 or combination of clad and vessel wall caninclude a J-shaped groove. The weld 109 can be formed in the groove toweld the pressure vessel 100 to the nozzle 10. It is to be understood,however, that various welds can be used to weld the pressure vessel 100to the nozzle 10.

As shown in FIG. 2, during an initial stage of the mid-wall repairprocess, a length of the nozzle 10 on an exterior side of the pressurevessel 100 can be removed. In a preferred embodiment, the nozzle 10 canbe cut by an abrasive cutting operation commencing on the exteriorsurface 13 of the nozzle 10. It is to be understood that the variousmaterial and component removal processes, including abrasive grindingand cutting, can be performed manually (i.e., by hand or with handtools) or remotely (i.e., by automatic tools or processes, includingthose in use or those that are later developed). As shown in FIG. 2, theheater or other component 20 can then be removed from the interior ofthe nozzle 10, decontaminated, and otherwise repaired or replaced,depending on its condition.

As shown in FIG. 3, the length of the nozzle 10 extending from theexterior surface 103 of the pressure vessel 100 can be further reduced.Returning to FIG. 2, a spacer barrier can be disposed within a portionof the nozzle 10 extending above the clad 107 in the interior of thepressure vessel 100 prior to the further reduction of the length. Thisspacer barrier is a foreign materials exclusion (FME) device to preventintrusion of foreign materials from the subsequent repair operationsinto the interior of the vessel. In a preferred embodiment, an abrasivecutting operation commencing on the exterior surface 13 of the nozzle 10can be used to further reduce the length of the nozzle 10. Preferably,the length of the nozzle is reduced to a predetermined length as closeas practical to the curved exterior surface 103 of the pressure vessel100.

As shown in FIG. 4, the nozzle 10 can be severed at a position adjacentthe mid-wall 105 of the pressure vessel 100 (i.e., between the interiorand exterior surfaces 101 and 103) to provide an upper nozzle portion17, which is welded to the pressure vessel 100 by the weld 109, and alower nozzle portion 19, which is no longer connected to the pressurevessel 100. In a preferred embodiment, the nozzle 10 can be severed byan abrasive cutting operation commencing on the interior surface 15 ofthe nozzle 10. In the preferred embodiment, the nozzle 10 can be severedat a predetermined distance from the bottom of the nozzle 10 thatmaximizes the lower nozzle portion 19 that will subsequently be removed.

As shown in FIG. 5, the lower nozzle portion 19 can be removed from thepressure vessel 100. In a preferred embodiment, the lower nozzle portion19 can be removed manually. The lower nozzle portion 19 can be removedfrom the pressure vessel 100 with a slide hammer or other means if itcannot be removed manually.

As shown in FIG. 6, the upper nozzle portion 17 can remain welded to thepressure vessel 100, and the FME device can be removed from the uppernozzle portion 17. The upper nozzle portion 17, as well as a portion ofthe mid-wall 105 exposed by removal of the lower nozzle portion 19 anddefining a mid-wall void 113, can be treated, cleaned, or otherwiseprepared for subsequent attachment of a replacement nozzle and insertionof a heater or other implement after cleaning the upper nozzle portion17. In a preferred embodiment, scale or other sediment can be removedfrom the upper nozzle portion 17, and a surface of the mid-wall void 113can be cleaned by an abrasive operation. More preferably, an abrasivegrinding wheel can be used to clean the upper nozzle portion 17 and thesurface of the mid-wall void 113. When access can be permitted to theupper nozzle portion 17 from the interior of the pressure vessel 100, acap (not shown) can be disposed to cover the upper nozzle portion 17,such that scale or other sediment removed from the upper nozzle portion17 or the mid-wall void 113 is prevented from contaminating the pressurevessel 100.

After cleaning the upper nozzle portion 17 and the mid-wall void 113,the surface of the mid-wall void 113 can be evaluated after dyepenetrant testing, to confirm that the surface of the mid-wall void 113,such as a portion of the surface adjacent the upper nozzle portion 17,is acceptable for subsequent installation of the replacement nozzle, asdescribed below.

As shown in FIG. 7, an alignment tool 40 can be disposed in the uppernozzle 17 to facilitate alignment and attachment of a replacement nozzle30 with the pressure vessel 100. The installation tool 43 can include ahead portion 41 having an outer diameter corresponding to a diameter ofthe mid-wall void 113, and having a flat surface configured to contactan end surface of the upper nozzle portion 17. By this arrangement, theinstallation tool 43 can axially locate the alignment tool in the uppernozzle 17 and the self-centering feature of the alignment tool locatesit radially relative the upper nozzle 17 with a high degree ofprecision.

In an embodiment of the invention, the alignment tool 40 can include asealing portion that seals against an interior surface of the uppernozzle portion 17. Such an alignment tool 40 can permit reactor fueloff-load or refueling while the mid-wall repair is occurring, bypermitting the pressure vessel 100 to be filled with water during therepair process of up to the removal of the alignment tool 40 andreinsertion of the heater or instrument.

As shown in FIG. 8, the replacement nozzle 30 can be disposed on analignment shaft 42 piloted in the alignment tool 40, and can beprecisely axially and radially located as described above. In apreferred embodiment, the material of the replacement nozzle 30 can bedetermined so as to resist stress corrosion cracking when thereplacement nozzle 30 is welded to the mid-wall 105, and more preferablya material of the replacement nozzle 30 can include Alloy 690 orstainless steel.

As shown in FIG. 9, at least one clamping device 50 can be used tomaintain the precise axial and radial position of the replacement nozzle30 in the mid-wall void 113. The clamping device 50 can include an endportion configured to retain the replacement nozzle 30, and can includean opposite end portion configured to retain another one of the nozzles10 or other available attachment point(s). By this arrangement, it isunderstood that the replacement nozzle 30 can be maintained at a desiredposition relative to other nozzles welded to the pressure vessel 100 orsome other desired alignment. In a preferred embodiment, a plurality ofclamping devices 50 are used to maintain the position of the replacementnozzle 30, and more preferably at least three clamping devices 50 areused.

The alignment tool 40 and alignment shaft 42 can be removed from theupper nozzle 17 and the replacement nozzle 30, such that the clampingdevice maintains the position of the replacement nozzle 30 relative tothe pressure vessel 100.

As shown in FIG. 10, the replacement nozzle 30 can be welded to themid-wall 105 of the pressure vessel 100, and more specifically a weld115 having at least three weld layers can be formed between the surfaceof the mid-wall void 113 and the replacement nozzle 30. In a preferredembodiment, the weld 115 can include a plurality of weld layers eachhaving a predetermined deposit height, and more preferably can includeat least three weld layers with a total predetermined deposit height ofat least 0.125 inches, and the overall buildup of the weld 115 can bedetermined such that the weld 115 extends only minimally beyond an innerdiameter of the replacement nozzle 30.

A welding tool 60 can be used to provide the weld 115 between thereplacement nozzle 30 and the mid-wall 105. The welding tool 60 caninclude a video camera such that a technician can monitor formation ofthe weld 115, a wire feed through which the technician can deliver amaterial for the weld 115, an inert gas delivery system to aid information of the weld 115, and a water cooling system for cooling thewelding tool 60.

A surface of the weld 115 can be prepared for subsequent testing andevaluation. After formation of the weld 115, the weld surface can beprepared for subsequent testing and evaluation. An abrasive grindingoperation can be used to remove an excess portion of the weld 115 (e.g.,a portion of the weld extending beyond the inner diameter of thereplacement nozzle 30).

The weld 115 can be inspected to determine the sufficiency of the weld115. In a preferred embodiment, the weld 115 can be liquid penetrantinspected.

In a preferred embodiment, the weld 115 can be ultrasonically inspected.More preferably, an ultrasonic map indicating properties of the weld 115can be provided, the map including characteristics of portions of theweld 115 such as echodynamic signature including response amplitude andtime of flight of the ultrasonic signal. By comparing the ultrasonic mapof the weld 115 with a plurality of ultrasonic maps of known defect-freeand defective welds, a technician can determine whether the weld 115 issubstantially free of defects. The ultrasonic maps of known defect-freeand defective welds can be determined by producing ultrasonic maps ofvarious weld samples, and then by destructively evaluating the weldsamples to determine the absence or existence of defects. It isunderstood that the term “defect-free” can include welds that meet orexceed the UT examination standards set forth in ASME Code, Section III,and specifically Paragraph NB-5330, which is hereby incorporated byreference. This is in contrast to the more forgiving UT examinationrequirements of ASME Code, Section XI, which is invoked for this repairby ASME Code Case N-638, which are also both hereby incorporated byreference. It is also to be understood that the above-described processcan be performed to provide a weld that exceeds ASME Code, Section XIrequirements.

Numerous additional modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, thepresent invention may be practiced otherwise than as specificallydescribed herein.

1. A method of repairing and inspecting a first nozzle penetrating aclosed vessel, comprising: removing a portion of the first nozzle;forming a weld between a replacement nozzle and a surface of themid-wall of the vessel; and evaluating the integrity of the weld at themid-wall of the vessel.
 2. The method according to claim 1 whereinevaluating comprises performance of a liquid penetrant test of the weld.3. The method according to claim 1, wherein evaluating comprisescomparing a characteristic of the weld to a characteristic of at leastone of a known defective weld and a known defect-free weld.
 4. Themethod according to claim 1, wherein evaluating comprises comparing acharacteristic of the weld obtained through ultrasonic inspection. 5.The method according to claim 4, wherein evaluating comprises comparingat least one of an echodynamic signature including response amplitude ofan ultrasonic signal and time of flight of the ultrasonic signalobtained by an ultrasonic inspection of the weld.